diff --git a/proc/library.map b/proc/library.map
index a38627b7..b438849e 100644
--- a/proc/library.map
+++ b/proc/library.map
@@ -10,7 +10,7 @@ global:
   openproc; closeproc;
   tty_to_dev; dev_to_tty; open_psdb_message; open_psdb; lookup_wchan;
   display_version; procps_version; linux_version_code;
-  Hertz; smp_num_cpus; have_privs;
+  Hertz; smp_num_cpus; have_privs; getbtime;
   sprint_uptime; uptime; user_from_uid; print_uptime; loadavg;
   pretty_print_signals; print_given_signals; unix_print_signals; signal_name_to_number; signal_number_to_name;
   meminfo; vminfo; getstat; getdiskstat; getpartitions_num; getslabinfo; get_pid_digits;
diff --git a/proc/sysinfo.c b/proc/sysinfo.c
index cd59534b..7ef68c53 100644
--- a/proc/sysinfo.c
+++ b/proc/sysinfo.c
@@ -90,6 +90,35 @@ int uptime(double *restrict uptime_secs, double *restrict idle_secs) {
     return up;	/* assume never be zero seconds in practice */
 }
 
+unsigned long getbtime(void) {
+    static unsigned long btime = 0;
+    FILE *f;
+
+    if (btime)
+	return btime;
+
+    /* /proc/stat can get very large on multi-CPU systems so we
+       can't use FILE_TO_BUF */
+    if (!(f = fopen(STAT_FILE, "r"))) {
+	fputs(BAD_OPEN_MESSAGE, stderr);
+	fflush(NULL);
+	_exit(102);
+    }
+
+    while ((fgets(buf, sizeof buf, f))) {
+        if (sscanf(buf, "btime %lu", &btime) == 1)
+            break;
+    }
+    fclose(f);
+
+    if (!btime) {
+	fputs("missing btime in " STAT_FILE "\n", stderr);
+	exit(1);
+    }
+
+    return btime;
+}
+
 /***********************************************************************
  * Some values in /proc are expressed in units of 1/HZ seconds, where HZ
  * is the kernel clock tick rate. One of these units is called a jiffy.
diff --git a/proc/sysinfo.h b/proc/sysinfo.h
index e30a38b9..97ae818f 100644
--- a/proc/sysinfo.h
+++ b/proc/sysinfo.h
@@ -17,6 +17,7 @@ extern void eight_cpu_numbers(JT *uret, JT *nret, JT *sret, JT *iret, JT *wret,
 #endif
 
 extern int        uptime (double *uptime_secs, double *idle_secs);
+extern unsigned long getbtime(void);
 extern void       loadavg(double *av1, double *av5, double *av15);
 
 
diff --git a/ps/output.c b/ps/output.c
index b4905c2b..338cf1a4 100644
--- a/ps/output.c
+++ b/ps/output.c
@@ -77,7 +77,6 @@ static unsigned max_leftward = 0x12345678; /* space for LEFT stuff */
 static int wide_signals;  /* true if we have room */
 
 static unsigned long seconds_since_1970;
-static unsigned long time_of_boot;
 static unsigned long page_shift;
 
 
@@ -813,7 +812,7 @@ static int pr_bsdtime(char *restrict const outbuf, const proc_t *restrict const
 static int pr_bsdstart(char *restrict const outbuf, const proc_t *restrict const pp){
   time_t start;
   time_t seconds_ago;
-  start = time_of_boot + pp->start_time / Hertz;
+  start = getbtime() + pp->start_time / Hertz;
   seconds_ago = seconds_since_1970 - start;
   if(seconds_ago < 0) seconds_ago=0;
   if(seconds_ago > 3600*24)  strcpy(outbuf, ctime(&start)+4);
@@ -927,7 +926,7 @@ static int pr_pmem(char *restrict const outbuf, const proc_t *restrict const pp)
 
 static int pr_lstart(char *restrict const outbuf, const proc_t *restrict const pp){
   time_t t;
-  t = time_of_boot + pp->start_time / Hertz;
+  t = getbtime() + pp->start_time / Hertz;
   return snprintf(outbuf, COLWID, "%24.24s", ctime(&t));
 }
 
@@ -950,7 +949,7 @@ static int pr_stime(char *restrict const outbuf, const proc_t *restrict const pp
   our_time = localtime(&seconds_since_1970);   /* not reentrant */
   tm_year = our_time->tm_year;
   tm_yday = our_time->tm_yday;
-  t = time_of_boot + pp->start_time / Hertz;
+  t = getbtime() + pp->start_time / Hertz;
   proc_time = localtime(&t); /* not reentrant, this corrupts our_time */
   fmt = "%H:%M";                                   /* 03:02 23:59 */
   if(tm_yday != proc_time->tm_yday) fmt = "%b%d";  /* Jun06 Aug27 */
@@ -961,7 +960,7 @@ static int pr_stime(char *restrict const outbuf, const proc_t *restrict const pp
 static int pr_start(char *restrict const outbuf, const proc_t *restrict const pp){
   time_t t;
   char *str;
-  t = time_of_boot + pp->start_time / Hertz;
+  t = getbtime() + pp->start_time / Hertz;
   str = ctime(&t);
   if(str[8]==' ')  str[8]='0';
   if(str[11]==' ') str[11]='0';
@@ -1982,7 +1981,6 @@ void init_output(void){
   // available space:  page_size*outbuf_pages-SPACE_AMOUNT
 
   seconds_since_1970 = time(NULL);
-  time_of_boot = seconds_since_1970 - seconds_since_boot;
 
   meminfo();